In angioplasty, a balloon catheter is generally inserted into a patient's vasculature percutaneously, usually into a femoral or radial artery. The balloon is then advanced until it reaches the treatment site, at which there is usually a stenosis or other occlusion, and expanded to compress or displace the stenosis and improve the flow of blood. In some procedures, the expandable balloon can carry a stent to be expanded at the occlusion site.
To efficiently and accurately advance a balloon catheter to a treatment site, guide catheters and guidewires are often positioned first. A balloon catheter may then be advanced over a guidewire and through a guide catheter. Consequently, a typical balloon catheter is constructed in the following manner. There is an inner tubular member having a lumen for a guidewire. This tubular member has an opening at the distal end of the balloon catheter for the introduction of the guidewire, and a more proximal opening for the egress of the guidewire. Disposed over this inner tubular member is an outer tubular member; the annular space between the first tubular member and the outer tubular member forms an inflation lumen for the balloon. A distal end of the balloon is sealed to the first tubular member and a proximal end is sealed to the outer tubular member.
The inner tubular member typically has a distal portion, often approximately the length of the balloon, that extends beyond the distal end of the outer tubular member. Thus, the distal portion of the balloon catheter may include only the distal portion of the inner tubular member and the balloon. This may make the distal end of the balloon catheter more flexible than may be desired. Also, when the balloon catheter is advanced through a patient's vasculature, much of the force resisting the advance of the balloon catheter is acting on this distal portion of the inner tubular member. This may cause the inner tubular member and the balloon to prolapse within the outer tubular member.
U.S. Pat. No. 5,425,712 to Goodin, entitled “Dilation Catheter Having Soft Bumper Tip”, herein incorporated by reference, alleviates some of these issues. It discloses a catheter including the features described above. Goodin also discloses bonding the inner tubular member to a distal portion of the outer tubular member adjacent to the proximal neck portion of the balloon. This provides additional support for the distal end of the balloon catheter.
However, this also creates a balloon catheter in which both the proximal and distal ends of the balloon are fixed to the inner tubular member. It has been found that balloons grow longitudinally during inflation at least 2% and sometimes up to 10%. If the inner tubular member is not attached at the proximal end of the balloon, the entire length of the inner tubular member can accommodate this growth, resulting in a low strain that is under the elastic limit of many materials common to this application. However, if the inner tubular member is attached at the proximal end the balloon, as is the case, for example, in Goodin, only the distal section of the inner tubular member, which is a much shorter segment, is free to accommodate this growth. This results in a significantly higher strain over this distal section, and this strain may be over the elastic limit of many of the materials used in this application.
U.S. Pat. No. 6,066,157 to Barbere entitled “Anchor Joint for Coaxial Balloon Dilation Catheter” attempts to address this problem by its balloon catheter. Barbere proposes a balloon catheter having a distal balloon, an outer catheter and an inner catheter, with the inner catheter defining a guidewire lumen, and the inner and the outer catheters defining an inflation lumen. The outer tubular member tapers distally and ends near an abutment member disposed on the inner tube in the balloon. This allows the inner catheter to move distally during expansion and prevents the abutment member, and consequently the inner member, from moving proximally. The abutment member creates an area of increased stiffness in the balloon portion.
It would be desirable to provide a balloon catheter which can provide additional distal support, yet avoid higher strain on a portion of the balloon catheter.